Reactor vessel for manufacture of superconducting films

ABSTRACT

Methods and reactors are described for the production of high temperature superconductor films on a variety of substrates, particularly those films which include volatile components during their manufacture. The reactors are particularly useful for producing films containing thallium. The reactors provide for relatively low volume cavities in which the substrate is disposed, and control of the thallium oxide overpressure during the processing. In a preferred embodiment, one or more holes or apertures are made in the reactor to permit thallium and thallium oxide to controllably leak from the reactor. For manufacture of double sided superconducting films, a reactor is used having top and bottom plates each with one or more holes in them. Uniform high temperature superconducting films are obtained while inhibiting reaction between the substrate and superconducting film during the processing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.07/516,078, filed Apr. 27, 1990, now U.S. Pat. which is acontinuation-in-part of Ser. No. 308,149, filed Feb. 8, 1989, nowabandoned, which is a continuation-in-part of application Ser. No.238,919, filed Aug. 31, 1988, now U.S. Pat. 5,071,830.

INTRODUCTION

1. Technical Field

The field of this invention is the production of high temperaturesuperconductor films which contain volatile components, such asthallium. More particularly, it relates to useful methods and devicesfor manufacturing superconductor films, particularly large area anddouble sided films.

1. Background

After the initial excitement of being able to produce high temperaturesuperconductors, namely materials which are superconducting above thevaporization temperature of nitrogen, the problems of producing thesematerials in useful form have become only too evident. Among the cupratecompositions which are particularly interesting because of their highsuperconducting transition temperature are the thallium compounds. Thesecompounds are particularly difficult to prepare because of the nature ofthallium oxides. Tl₂ O₃ is unstable, so that at the elevated processingtemperatures normally employed, it decomposes to Tl₂ O and O₂. In orderto maintain the thallium present in the oxide mixture used to form thesuperconductor, it is necessary to control the amount of thallium in thevapor phase and in the liquid phase of the oxide compositions. Among theother difficulties with processing thallium is that thallium is highlyreactive, so that reactors which are employed must take into account thereaction of the structural materials with thallium. One is thereforeconfronted with working with a highly reactive material which can existin both the vapor and liquid phases simultaneously at elevatedtemperatures, while trying to control the distribution of the thalliumbetween the liquid and vapor phases in order to obtain the appropriatecompositions for a high temperature superconductor.

For many applications, one wishes to have a thin high temperaturesuperconducting film on a substrate. Among the substrates are magnesiumoxide, lanthanum aluminate, yttria stabilized zirconia and sapphire. Formicrowave device development, sapphire has many advantages includingextremely low loss tangent at low temperature, availability in largearea substrates, low cost and general acceptance as a microwavesubstrate. In addition, for low loss films on sapphire, several ordersof magnitude improvement in the Q of a microwave device can still beachieved as high temperature superconducting films are improved.However, formation of thallium high temperature superconducting films onsapphire are subject to reaction and formation of barium aluminatecompounds as second phases.

There is substantial interest in being able to produce thallium cupratehigh temperature superconducting films on a wide variety of substratesfor production of microwave and millimeter wave applications. It istherefore of interest to provide processes and reactors which will allowfor the controlled and reproducible production of high temperaturesuperconducting films on substrates of interest for the production ofdevices.

The earliest attempts to manufacture thallium containing hightemperature superconductors focused on bulk formation as opposed to thinfilm formation. Recognizing volatility of thallium, some workers optedto enclose the amorphous precursor deposit and substrate within a sealedvessel to reduce thallium loss. For example, Engler et al, U.S. Pat. No.4,870,052 recites the formation of a bulk thallium containingsuperconductor by the mixing together of oxides and heating in apreheated oven in a closed vessel in the presence of oxygen for from 1to 5 hours at a temperature from 850° to 900° C. Engler most prefers theclosed vessel be a sealed quartz vessel. The sample of admixed metaloxides may be held in a crucible, made for example from gold, silver,platinum, aluminum oxide or zirconium oxide and sealed inside the quartzvessel. Engler notes that even when the reaction is carried out in asealed vessel, approximately 20% of the thallium is lost due to thevolatilization and reaction with the quartz. Similarly, Gopalakrishnan,U.S. Pat. No. 4,929,594 suggests heat treatment of the mixed reactantsin a tube made of non-reacting metal such as gold where the tube iswelded shut. Alternatively, other workers have followed apost-composition heat treatment process in which there is no containmentof volatile species. For example, Hermann et al, U.S. Pat. No. 4,962,083discloses a preparation technique in which the mixed oxides are pressedinto a pellet which is placed in a preheated tube furnace, having oxygenflowing therethrough. Studies have been reported in which thehigh-temperature heat treatment has been conducted under a variety ofconditions, including use of an opened crucible versus a covered orsealed crucible. See e.g., Lee et al, "Superconducting Tl-Ca-Ba-Cu-OThin Films With Zero Resistance at Temperatures of Up to 120 K",Appl.Phys.Lett., 53 (4), Jul. 25, 1988, p. 329-331.

The earliest high temperature superconducting films formed wererelatively small, having diameters often well less than 1 centimeter. Itis highly desirable to make larger area films for many applications.Current commercially available substrates are larger than 1 centimeter,some such as lanthanum aluminate being available in up to 2 inchdiameters. It is desirable to be able to use the largest availablesubstrates to form high temperature superconducting films.

It is further desirable to manufacture double-sided films, that is, asubstrate having superconductive material on multiple surfaces.Formation of such films has been extremely difficult, since processingtechniques used to perfect the superconducting properties for one sideof the film have damaged the superconducting properties of the otherside of the film. Previously, it has been virtually impossible torepeatably form commercial grade double-sided high temperaturesuperconducting films.

SUMMARY OF THE INVENTION

Methods and reactors are provided for the production of high temperaturesuperconducting films which contain volatile materials such as thalliumby providing for controlled leakage of the volatile material or itscompounds from the manufacturing vessel. The vessel includes anintentional leak, which may be repeatably formed. Desired morphology andsuperconducting phase is engineered by control of the temperatureprofile, oxygen pressure, diffusion rate out of the reactor and startingcomposition of the precursor film. Use of a relatively small volumevessel permits rapid equilibrium to be achieved between the film andvapor.

In one preferred embodiment, the reactor comprises a bottom plate,spacer and a top plate, having one or more apertures to permit leakageof the volatile components out of the reactor vessel. For themanufacture of larger area films, the top plate is preferably providedwith a plurality of holes to permit escape of the volatile components.For smaller films, a single aperture may be sufficient.

Substrates having high temperature superconductors on both sides may bemanufactured in a vessel wherein the top and bottom plates contain oneor more apertures each. Preferably, thermal contact between thesubstrate and the vessel is minimized, such as through the use of pointcontact pins. In the preferred method of manufacture, the coatedsubstrate is heated to the desired temperature, with the heating rateapproaching the maximum temperature being relatively low.

By employing the subject heating profile and reactors, high temperaturesuperconducting films on a variety of substrates may be reproduciblyobtained. Most specifically, any size of substrate, whether of large orsmall area, may be used. Further, double-sided films may be formed.

Accordingly, it is a principal object of this invention to provideapparatus and techniques for the production of superconducting films ofany size.

It is a further principal object of this invention to permit themanufacture of double-sided superconducting films.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view including cut-out of a reaction vessel andsubstrate.

FIG. 2a and 2c are plan views of the top piece of the reaction vessel ofFIG. 1, including two cross-sections.

FIG. 3 is a perspective view including cut-away for a reaction vesseland substrate.

FIG. 4 is a plan view of a top piece for a reaction vessel havingmultiple aperatures.

FIGS. 5a and 5b are spacer rings for a reaction vessel particularlyadapted for production of double-sided films, including cross-section.

FIGS. 6a and 6b are plan views of another embodiment for a spacer ringparticularly adapted for the manufacture of double-sided films,including cross-section.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Methods and apparatus are provided for the reproducible production ofhigh temperature superconducting films which include a relativelyvolatile component at some stage during the film's manufacture. The mostimportant examples are thallium based cuprate films on a wide variety ofsubstrates. However, the apparatus and techniques disclosed here aregenerally useful for forming superconducting films, particularly thosewith volatile components. For ease of explanation, the description whichfollows will focus on the formation of thallium based superconductors.

The methods employ apparatuses which allow for controlled increase intemperature to a predetermined elevated temperature, maintenance at thepredetermined temperature and relatively rapid cooling substantiallybelow the predetermined temperature. In addition, the apparatuses aredesigned to maintain controlled thallium oxide and oxygen pressures overthe film forming composition, whereby formation of the superconductingcomposition occurs with precipitation of the superconducting film from amelt. The resulting products comprising the high temperaturesuperconductor thallium cuprate based films on a variety of substratesfind use in microwave and millimeter wave devices, where highsuperconducting transition temperatures, low surface resistance on lowloss tangent substrates, such as MgO, LaAlO₃, LaGaO₃, or sapphire, andshort penetration depths are necessary or desirable.

The films provided for in this invention are comprised of thallium,calcium, barium and copper oxides. The stoichiometry may include 2021,2122, 2223, or such other stoichiometries as may provide forsuperconductivity. The films may be oriented films, so as to have asubstantially uniform crystallinity. The films may be comprised of asingle crystal or a plurality of crystals joined at their grainboundaries. The films may be highly oriented with the c-axissubstantially normal to the surface of the substrate as demonstrated byX-ray analysis or electron beam channeling techniques. For the mostpart, single phase films will be obtained, although as desired, mixturesof two of the phases or related phases may be achieved within the film.For some applications, polycrystalline films may be prepared. Dependingon the substrate, epitaxial films may be obtained.

The thickness of the film may be controlled. The film may be as thin asone layer, where the layer includes all of the necessary planes toobtain superconductivity, generally from about 30-50 Å or may be asthick as two micrometers or greater, depending upon the particularapplication. Thin films may be conveniently prepared by initiallypreparing a thicker film and then reducing the thickness, e.g., by ionmilling. The thickness of the film is primarily a practicalconsideration, rather than a significant limitation of the proceduresemployed depending upon the characteristics for current density andpenetration depth.

For many uses, a fraction of a micrometer thickness will be employed,generally in the range of about 0.1-1 μm. The film will have asuperconducting transition temperature of at least 75K, more usually90K, preferably at least at 100K, more preferably about 115K, andparticularly preferred at least about 122K, where the transitiontemperature has so far been substantially less than about 150K. 2122composition films can be achieved with T_(c) of at least 105K and can be110K or higher and 2223 films with a T_(c) of at least 110K or higherand 2223 films with a T_(c) of at least 110K and can be 122K or higher.The superconducting transition temperature should be as high asfeasible, though in some situations one parameter may be compromised foranother parameter. For the most part the films will be used attemperatures in the range of about 60-110K.

The films will usually have critical current densities at 77K of atleast about 10³ A/cm², usually at least about 10⁶ A/cm². For microwaveand millimeter wave applications, the surface resistance or impedancewill generally be less than about 10⁻³ Ω, more usually less than about10⁻⁴ Ω, at 10 GHz and at a temperature above 50K, preferably above about75K.

A wide variety of substrates may be employed, such as magnesium oxide,lanthanum aluminate, yttria stabilized zirconia, lanthanum gallate,lanthanum strontium aluminate, sapphire, buffered sapphire, metals, suchas Ag, Au, Pt, or other reactive or inert substrates. The subject methodfinds particular application, with reactive substrates, where theprocessing allows for minimal reaction between the high temperaturesuperconductor precursor layer and the substrate.

Generally, the overall method for formation of superconducting films inconnection with the disclosed apparatus and method comprise a two stepprocess:

(1) Formation of a superconducting precursor film on the substrate, and

(2) Post-deposition thermal processing to form a superconducting film.

The precursor film may be formed by any known technique, such as bysol-gel, laser ablation, thermal evaporation, liquid phase epitaxy,electron beam or magnetron sputtering, or chemical vapor deposition. Thesol-gel and laser ablation techniques are described in detail in U.S.patent applications Ser. No. 308,149, filed Feb. 8, 1989, entitled:LIQUID PHASE THALLIUM PROCESSING AND SUPERCONDUCTING PRODUCTS, and Ser.No. 238,919, filed Aug. 31, 1988, entitled: SUPERCONDUCTOR THIN LAYERCOMPOSITIONS AND METHODS, both of which are incorporated herein byreference.

Once the film has been formed, a relatively strict temperature regimenwill be employed for the heating of the film to provide the propercomposition for the high temperature superconductor film. Generally,controlled, uniform heating will be employed to achieve a predeterminedtemperature in the range of about 800° to 900° C., more usually about800° to 860° C. For the 2122 phase, heating to temperatures less than850° C. have proved sufficient, with temperatures less than 835° C.being more preferred, and a maximum temperature of 820° C. being optimalfor optimization of certain device characteristics. The heating rateshould be carefully controlled and uniform over the entire substrate.The heating rate controls two key film processing characteristics: a)degree of melting, and b) Tl₂ O evaporation rate from the film. The morerapid the heating rate employed, the more completely melting isobserved. In extreme cases for very T1 rich deposit compositions, rapidheating rates will result in films with a splotchy appearance and poorsubstrate coverage. The rate of heating will usually be at least about5° C./min., and may be as high as 200° C./min. or higher, usually in therange of 5° to 40° C./min. The time for which the temperature ismaintained will generally range from about 0.5-300 min. The temperaturewill then be dropped at a rate in about the same range as the rate ofheating.

There are a number of parameters which can be varied in relation to thethallium and oxygen present in the film and the cavity. One can providefor excess thallium in the superconducting film precursor, as a film onthe wall of the cavity, or by introduction of thallium oxide from anoutside source. Alternatively, one may remove thallium oxide from thecavity by providing for a chemical thallium oxide sink on the walls ofthe cavity or by providing for a conduit into the cavity which allowsfor removal of thallium oxide from the cavity. In addition, one may varythe oxygen over pressure in the cavity, which will affect the volatilityof thallium oxide in the film or source. Thus, by varying the thalliumoxide in the cavity which will be directly related to the amount ofthallium oxide in the precursor film, one can control the formation andcomposition of the high temperature superconducting film.

The devices of the subject invention will have means for controlling thetemperature profile of the process, so that the desired rate ofheating/cooling can be achieved with desired maintenance at thepredetermined elevated temperature. In addition, means are provided forcontrolling the thallium and thallium oxide overpressure, which meansmay include controlling the oxygen overpressure, as well as providingfor a source of sink of thallium oxide within the reactor cavity. Inaddition, the volume of the reactor cavity is controlled, so as to bepreferably only a small multiple of the volume of the superconductingfilm precursor and access to the cavity can be provided with means forintroducing or removing the volatile components present in the cavity.

A number of reactor designs are described in detail below. Generally,the reactor designs permit controlled leakage of volatile components,such as thallium and thallium oxide, from the reactor vessel, resultingin a crystal having the desired amount of thallium.

FIG. 1 shows a perspective view including cut-out of a reactor vesseluseful for post-deposition processing of precursor deposits on asubstrate. Generally, the reaction vessel comprises a base 10, spacerring 12, top plate 14 and cover plate 16. A substrate and precursor film22 are disposed within the reaction chamber. Generally, the reactionvessel of FIG. 1 provides a path for communication between the spaceadjacent the substrate 22 and external of the reaction vessel.

In the preferred embodiment, the components of the reaction vessel aremade of polished sapphire. However, any material compatible with thetemperature requirements and sufficiently nonreactive to thallium oxidemay be used. In the embodiment shown, the components are circular, doneso for ease of manufacture, but may be of any desired shape.

In the form shown, all of the components have an outside diameter of oneinch. The base 10 has a thickness of 0.013 inches. The spacer ring 12has a thickness of 0.125 inches and an inside diameter of 0.8 inches.The top plate is 0.013 inches thick and has a 0.15 inch diameter holelocated at its center. The cover plate 16 is 0.040 inches thick and hasa trench 20 of depth 0.020 inches and width 0.030 inches.

FIG. 2 shows a plan view of the cover plate 16. The cross-section atline A--A shows the trench 20. The cross-section at line B--B shows thetrench in cross-section. The trench in the cover plate 16 is placed overthe hole 18 in the top piece 14. The volatile vapors from the precursorfilm and substrate 22 may exit the reactor vessel via the hole 18 andchannel 20 to a portion exterior to the reaction vessel.

Six principal methods may be used to control the rate of thallous oxidevaporization from the deposit which occurs during thermal processing.The first involves changing the amount of empty volume present in thecavity. This can be controlled by varying the thickness of the spacer orby placing inert spacers to take up excess volume in the reactor. Asecond method involves increasing the process temperature to increasethallium volatilization. A third method is to change the overall oxygenpartial pressure during a particular time-temperature process sequence.Since oxygen actively suppresses volatilization of thallous oxide,lowering the total system pressure is an effective mechanism forincreasing thallium volatilization at any given temperature. A fourthmethod is to vary the spacing between the individual substrate layersthat make up the walls of the reactor. The greater the spacing betweenthe substrates, the greater thallium evaporation rate from the film. Forexample, if the sapphire reactor wafers are fitted tightly together,either by use of inconel clips or heavy weights placed on the lever arm,loss of thallium from the film is extremely small, even when held at860° C. in one atm of oxygen for reaction times of 8 min. or more. Onthe other hand, if the cap is omitted from the reactor, and the filmheated in an open crucible, thallium completely evaporates in a fewseconds. A fifth method for controlling thallium oxide vaporization isthe rate of heating. The faster the rate of heating, the more liquidthallium oxide present and the greater the amount of vaporization. Thesixth method involves the hold time and the elevated temperature. Thegreater the hold time, the more thallium oxide is vaporized and lost.

The use of extremely small reactor volumes guarantees rapid equilibriumbetween the film and vapor, thereby minimizing lateral composition ormorphological gradients in the film. The thermal process geometry isboth readily scalable and compatible with current available rapidthermal annealing furnace equipment. The thallous oxide vaporizationrate from the film can be controlled by varying the oxygen partialpressure, temperature and the diffusion-limited (leak rate-gappeddimensions) loss rate from the reactor.

FIG. 3 shows a reactor design which is particularly well adapted forthermal processing of large area wafers. Structurally, a top plate 34 isprovided with a plurality of holes 36 to permit escape of thallium andthallium oxide from the reactor vessel. A spacer ring 32 and bottomplate 30, in conjunction with top plate 34, define the relatively smallvolume in which the wafer having the deposited precursor film 38 isplaced. For a 2 inch wafer, typical dimensions for the top piece 34would be 3 inches in diameter, by 0.2 inches thick. The center spacer 32would have a 3 inch outside diameter and preferably 2.0125 inch insidediameter, with a thickness of 0.125 inches. The base plate 30 would havea 3 inch diameter with a thickness of 0.125 inches. These dimensions maybe appropriately modified to receive a wafer of any desired size.

In the preferred embodiment, the top piece 34, spacer 32 and bottompiece 30 are formed of sapphire crystals. Preferably, the crystals aredouble side polished to permit better sealing of the vessel whenassembled. Such sapphire crystals are available from Union Carbide. Inthe embodiment shown, there are five holes 36 each having a diameter of0.020 inches. One hole is located at the center of the top plate 34, andthe remaining holes are each located on a radius from the center hole,1/2 inch out.

Experimentally, the reactor of FIG. 3 has been used to producesuperconducting films on 2 inch diameter lanthanum aluminate wafers.Typically, a reactor station is utilized which includes a Lindberg 3zone 1200° C. furnace, an inconel pressure vessel, pressure controlsystem and vacuum pump. Generally, for microstructure control, it hasbeen found advantageous to heat the precursor film to a maximumtemperature of less than 850° C.

Formation of the superconducting films by this post depositionprocessing technique utilizes the controlled loss of thallium to achievethe desired end stoichiometry. Numerous factors may be used to controlthe rate of thallium loss. For example, the particular geometry of thereaction vessel, including the size of the holes, bears upon the rate ofthallium and thallium oxide loss. Further, the temperature profile maybe varied to optimize the film results. Generally, for thin filmdevices, it is desirable to avoid temperature gradients, which in turnindicates a relatively slower heating rate than a faster heating rate.Further, the oxygen pressure may be varied to control the thalliumvolatility.

FIG. 4 shows a top plate usable for reaction vessels having a pluralityof holes. Specifically, the embodiment shown in FIG. 4 has 61 holes. Theholes are 0.020 inches in diameter. As shown, they are spaced 0.2 inchesaway from their nearest neighbor. The distance "t" shown in FIG. 4 is0.1732 inches. The use of multiple holes has been found to promote evenvolatilization over the surface of the film and substrate. The use of alarger number of holes, relatively evenly distributed over the surfacehas been found particularly useful for formation of large area anddouble-sided films. Especially in the case of double-sided films, alower heating rate is used to avoid differential thermal expansion, andmultiple holes permit shorter holding time at elevated temperatures.Finally, the use of multiple holes has resulted in easier control of themicrostructure of the resulting superconducting film.

Spacer rings for reactors particularly useful for forming hightemperature superconductor films on both sides of a substrate are shownin FIGS. 5 and 6.

Generally, the reaction vessel will be defined by top and bottom piecesof any desired form, preferably as shown and described in connectionwith FIGS. 1 through 4. The spacer rings may be formed integral with theremaining components of the vessel, but have been shown here separatelyfor clarity and ease of explanation. In the embodiment of FIG. 5, aledge 52 is formed in the spacer 50 which supports the wafer (notshown). In the embodiment shown, the spacer ring 50 has an outsidediameter of 3 inches, and a minimum inside diameter of 1.9 inches. Theledge 52 is disposed generally half way down, with the depth of theledge being 0.055 inches. If desired, local spacers may be placed on theledge 52 so as to reduce the area of contact between the spacer ring 50and the wafer. In an alternative embodiment shown in FIG. 6, the wafer,not shown, is supported by essentially point contacts 62. The spacerring 60 includes projections 62 for supporting the wafer. Across-section of the support 62 is shown in FIG. 6. For the embodimentshown, the outside diameter of the spacer ring 60 is 3 inches, and theinside diameter is 2.25 inches. The projections 62 are approximately0.120 inches wide and contain a stepped profile where the side-to-sideinside diameter of the upper step is 2.01 inches and the inner faceinside diameter is 1.9 inches. For thin substrates it is particularlyimportant to avoid thermal gradients which might break the wafer. Ifinfrared heating is used to heat the wafer, and sapphire is used to formthe vessel, the wafer will absorb the infrared radiation to a muchhigher degree than will the sapphire vessel. The vessel may be coated tohave a higher absorptivity to infrared radiation, such as by coating thesapphire with metal, such a nichrome.

All publications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be readily apparent to those of ordinary skill inthe art in light of the teachings of this invention that certain changesand modifications may be made thereto without departing from the spiritor scope of the appended claims.

What is claimed is:
 1. A reactor vessel for thermal processing of adeposited metal oxide film including thallium on a substrate to becrystallized into a superconductor, comprising a vessel including achamber large enough to receive the substrate and film, the vesselincluding at least one aperture to permit controlled venting of thethallium.
 2. A reaction vessel for post-deposition thermal processing ofa film and substrate to be crystallized into a thallium containingsuperconductor, comprising:a top piece with one or more holes, a bottompiece, and a spacer for defining a chamber with the top piece and bottompiece, the chamber being large enough to accommodate the film andsubstrate.
 3. The reaction vessel of claim 2 wherein the top piece,bottom piece and spacer are formed of sapphire.
 4. The reaction vesselof claim 3 wherein the sapphire is coated to increase its absorption ofenergy.
 5. The reaction vessel of claim 3 wherein the coating isnichrome.
 6. The reaction vessel of the 2 wherein the top piece has twoor more holes.
 7. The reaction vessel of claim 6 wherein the top piecehas 5 holes.
 8. The reaction vessel of claim 2 wherein the bottom pieceincludes one or more holes.
 9. The reaction vessel of claim 2 whereinthe spacer includes support for the substrate.
 10. The reaction vesselof claim 9 wherein the support comprises a ledge formed in the spacer.11. The reaction vessel of claim 9 wherein the support provides forpoint contact between the spacer and the substrate.
 12. The reactorvessel of claim 2 further including reactor clips to hold the top piece,bottom piece and spacer together.
 13. The reaction vessel of claim 2further including a cover over at least one of the holes.
 14. Thereaction vessel of claim 13 wherein the cover includes a channel.
 15. Areaction vessel for forming superconductors on multiple sides of asubstrate comprising:an interior chamber adapted to hold the substrateon which precursor films have previously been deposited, a supportmember adjacent the interior chamber to support the substrate andprecursor films, and a passage between the interior chamber and theexterior of the chamber to permit controlled venting of volatilematerial.
 16. The reaction vessel of claim 15 wherein the support membercomprises an annular ledge formed in the surface of the interiorchamber.
 17. The reaction vessel of claim 15 wherein the support membercomprises a plurality of contact supports formed adjacent the surface ofthe interior chamber.
 18. The reactor vessel of claim 15 wherein theinterior chamber is defined by a top plate, a spacer and a bottom plate.19. The reactor vessel of claim 18 wherein the top plate and bottomplate each include one or more holes.